Can we use "any" with singular countable nouns? If so, what's the grammar rule? Can you share a link or a source so that I could refer ?
Ex-
01. There isn’t any issue.
02. There isn’t any student in the class?
03. Isn’t there any student in the class?
Are the above ssentences correct?
The site seems to contradict itself. First, it says "Do not use any' with singular countable nouns. It then says "It's more common to use 'isn't+a' for singular countable nouns".
There might be some truth to their second assertion; there isn't any reason to believe the first.
Yes, you can, and your examples are acceptable.
The three main uses are
[1] I haven't got any job lined up for you today, I'm afraid.
[2] I don't think any candidate expressed a view on this point.
[3] Any policeman will be able to help you.
You may encounter the terms 'non-proportional' to describe the sense of "any" in [1], 'proportional' for that in [2] and 'free choice' for that in [3].
Note that the count singular use in [1] is relatively rare.
I quickly tried to find a suitable resource on the 'Net, but they all said the same as the the one you cited.